1. Field of the Invention
This invention relates generally to the fabrication of a giant magnetoresistive (GMR) magnetic read head, more specifically to a method of fabrication that allows better control of the sensor read-width while still maintaining a high level of insulation between the sensor and the lower shield.
2. Description of the Related Art
As GMR (giant magneto-resistive) magnetic read heads are required to read recorded media having increased linear densities and track densities, the active read-width portions of these heads must become correspondingly thinner (thin read-gap) and narrower (narrow read-width). This requirement necessitates the formation of GMR sensor layers that are thin, highly planar and have narrow and accurately defined read-widths. The formation of such a sensor layer places stringent constraints on the insulation between the layer and the magnetic shield on which it is typically formed. One way of achieving the dual requirement of a thin, planar GMR layer with adequate layer-to-shield insulation, is by the formation of an insulation layer having “patches,” which are additional thicknesses of insulation in the regions to either side of the read-width region of the GMR layer. FIG. 1 (prior art) shows such a patch formation. Referring to FIG. 1a, there is shown a schematic cross-sectional view of a partially formed GMR read head, wherein a planarized lower shield (100) has sequentially formed upon it an insulating dielectric layer (120) and a GMR sensor layer (140). To either side of what will ultimately be the active portion of the sensor (the sensor read-width region), there are formed insulation patches (180), which provide an additional degree of insulating protection between the sensor layer (140) and the shield (100). The non-planar topology of this formation has negative consequences for the subsequent formation of conductive lead and biasing layers, which is the concern of the present invention.
Referring next to FIG. 1b, there is shown the consequences of depositing a polydimethylglutarimide (PMGI) layer (200) over the non-planar topology as a prior step in forming lead layers, biasing layers and upper shield layers. Such a PMGI layer is commonly formed as an initial step in the process of photolithographic stencil formation or other processes. In this case, the PMGI attains a non-planar profile with thickness variations shown by arrows (220, 240), which is disadvantageous for further processing.
Chen et al. (U.S. Pat. No. 6,307,721) disclose a thin read-gap, double layer sensor element having similar topology to the much simpler structure shown in FIG. 1 herein. The attempt to form a second GMR layer (FIG. 4 of Chen et al.) necessitates the formation of a lift-off stencil (38c and 38b of FIG. 4 of Chen) within a concavity. The use of such lift-off stencils is important for the formation (by deposition) of conducting lead layers and biasing layers an the lateral edges of a GMR sensor layer. Such stencils cannot accurately define the edges of the deposited layers and the “overspray” of the deposition beneath the stencil overhang can cause difficulties. Ju et al. (U.S. Pat. No. 6,287,476) teach a method of preventing current shunting through such overshoot regions by means of a passivation layer formed on the GMR layer surface.
Chen et al. (U.S. Pat. No. 5,491,600) also teach the use of a lift-off stencil formed of a lower pedestal of polydimethylglutarimide (PMGI) and an upper overhanging region of photoresistive material, to form lead and biasing layers against the lateral edges of a read sensor. The magnetoresistive sensor is not a GMR type sensor and its thinness, insulation from a lower shield and lateral definition are not as critical as in the devices addressed in the present invention.
Sato teaches a method of forming a thin film magnetic read head with a thicker lead layer by a process of forming a step in a lower shield layer, depositing an insulating layer over the stepped shield and then forming the sensor layer over the step portion. This method does not provide the planar surface topology of the present invention. Finally, Pinarbasi (U.S. Pat. No. 5,883,764), teaches the formation of a GMR sensor having multi-layered conducting leads. Like the teaching of Chen et al. (cited above), Pinarbasi teaches the use of a lift-off stencil to form the lead layers, but the requisite thinness of the sensor layer and its insulation from a lower shield is not a concern of the method.